A known electrochemical device, such as a battery and an electric double layer capacitor, includes an outer package and a power generating element housed in the outer package. The power generating element includes electrodes with active material layers formed on metal foil surfaces of the respective electrodes. In general, each electrode has a portion on which the active material layer is not formed and a current collector is connected to an electrode terminal provided for input and output of power.
In the known electrochemical device, a synthetic resin sheet is disposed between the power generating element and the outer package for vibration and impact protection purposes. However, such a sheet may not provide sufficient protection for the power generating element that may move inside the outer package when strong vibrations or a high impact is applied to the power generating element. As a result, the current collector may deform or stick into the power generating element. If that happens, an internal short-circuit may occur. To improve a safety level of the electrochemical device, vibration and impact resistance needs to be increased. Especially, when the power generating element is used for a vehicular battery, the power generating element requires considerably high resistance for vibrations that occur while the vehicle is running and for an impact that may be applied in a collision of the vehicle. Therefore, the improvement of the vibration and impact resistance is mandatory.